"Going to church could save your life," reports the Daily Mail, adding that, "Women who worship once a week are '25 per cent less likely to die early'." Perhaps surprisingly, while the first part of the headline is overly simplistic…

"Going to church could save your life," reports the Daily Mail, adding that, "Women who worship once a week are '25 per cent less likely to die early'."

Perhaps surprisingly, while the first part of the headline is overly simplistic, it may not technically be wrong – according to new research from the US, anyway. Whether or not divine providence is responsible for the increase in lifespan is still up for debate.

A large Harvard study showed that predominantly white Christian nurses who attended religious services more than once a week had a 33% lower relative risk of dying over a 16-year period compared with similar women who did not attend religious services.

A sizeable chunk of the link was explained by social support (23%), smoking rates (23%) and, to a lesser extent, optimism differences (9%) between attenders and non-attenders.

The study was very large, precise, and as robust to bias and confounding as you could reasonably expect, so it can be considered reliable. But the lifestyle and social differences between the groups can't go unnoticed.

It's therefore possible that the regular pattern of social interaction associated with being part of a religious community, and the benefits this brings, is mainly responsible for the outcome seen in this research, rather than any specific religious or spiritual aspects.

Atheists who regularly attend humanist gatherings, or just those who go to weekly bingo sessions, may also experience similar benefits.

Where did the story come from?

The study was carried out by researchers from the Harvard T. H. Chan School of Public Health in the US.

It was funded by the John Templeton Foundation, which, according to its website, funds research on the "big questions of human purpose and ultimate reality". The foundation has a stated aim of using scientific methods to explore the alleged spiritual aspects of reality.

The study was published in the peer-reviewed Journal of the American Medical Association: Internal Medicine.

Generally, the media covered the story accurately, citing the possible reasons why attending religious services might be good for you in terms of boosting social support, happiness and optimism.

For example, The Independent reported advice from the researchers, who said: "Our results do not imply that healthcare professionals should prescribe attendance at religious services, but for those who already hold religious beliefs, attendance at services could be encouraged as a form of meaningful social participation."

What kind of research was this?

This cohort study looked at the links between religious service attendance and subsequent death in female nurses.

This type of study is appropriate to investigate this link.

But many factors can influence death rates, and potentially also be linked to church attendance – for example, more resilient social networks can help people cope in times of hardship.

Teasing out any clear causal links from the vast mix of influencing factors is tricky.

What did the research involve?

This study analysed self-reported religious service attendance information from 1996 to 2012 and linked death records from the same time period.

The researchers analysed information from 74,534 female US nurses who had been answering health and lifestyle questionnaires every two years from 1992 to 2012 as part of the Nurses' Health Study, a rich ongoing source of epidemiological research.

From 1992 and every four years thereafter, women were asked how often they go to religious meetings or services. Responses included more than once a week, once a week, one to three times a month, less than once a month, and never (or almost never).

The researchers' main analysis looked at the death rates of women with different frequency of religious attendance, comparing them with those who did not attend.

They adjusted for a lot of confounders to try to isolate the single effect of religious attendance, including:

age

alcohol consumption

physical exercise

multivitamin use

high blood pressure

high cholesterol

use of hormonal replacement therapy

healthy eating scores

smoking status

body mass index

husband's education level

physical impairment

social integration score – composite of marriage status, group participation, number of close friends or relatives

living alone

family income

geographic region in the US

depression in 1992

religious attendance in 1992

The researchers also performed a "mediator" analysis, which helps understand how much each of the confounders is contributing to the main link of interest – in this case, religious service attendance and death.

What were the basic results?

Most women were either Roman Catholic or belonged to other Christian denominations, and 97% or more were white. There was a small minority of Jewish women and no Hindu or Muslim women.

There was a consistent pattern between religious service attendance and lower rates of death from any cause, cardiovascular disease and cancer.

There were 13,537 deaths over the study period, giving a base rate of death of 18.1 %. Compared with women not attending religious services, women who attended a service more than once a week had 33% less risk of dying from any cause during the 16-year study (hazard ratio 0.67, 95% confidence interval [CI] 0.62 to 0.71).

Those attending regularly in both 1996 and 2000 – a sign of long-term, regular attendance – had an even lower relative risk at 45% (95% CI 0.52 to 0.59) less than non-attenders.

Looking at potential mediators, the researchers picked out depressive symptoms, smoking, less social support and optimism as the most important.

Social support explained the highest proportion of the link (23%), with smoking a close second (22%). Optimism accounted for around 9%.

The link appeared consistent over time, as well as for religion (although there wasn't much variety), geography and other potentially influential factors.

How did the researchers interpret the results?

The researchers said that: "Frequent attendance at religious services was associated with significantly lower risk of all-cause, cardiovascular, and cancer mortality among women.

"Religion and spirituality may be an underappreciated resource that physicians could explore with their patients, as appropriate."

Conclusion

This study showed that white Christian women who attended religious services more than once a week had a lower risk of dying from any cause, cancer, and cardiovascular disease specifically compared with similar women who did not attend religious services.

This link was at least partially explained by social support, smoking rates, and optimism differences between attenders and non-attenders.

As the study was very large, it gives precise estimates of relative risks. The researchers pointed out there are other factors that could potentially mediate the link that they couldn't measure in their study, like psychosocial resilience, religious coping mechanisms, a sense of a purpose in life, and self-discipline.

But their interesting stats also showed that biases from these or other sources would have to be very large to affect the result in a meaningful way, suggesting the study's conclusions are quite solid.

The study mainly involved white women who mostly identified as Christian, so we don't know if the same effects would be seen for men of a similar faith, or adults or children from other religions or with no religion.

Non-religious groups could argue having a purpose in life, self-discipline and many other aspects that potentially mediate the link are not the sole preserve of the religious, but there is no doubt that for many people this comes from practising a faith.

But it's possible the same effect could be achieved in other ways, too. While the researchers tried to account for social factors associated with religious attendance, there could well be other unmeasured, or possibly unconsidered, effects associated with regular social group interaction.

A similar study could have noted reduced mortality among people attending any community activity groups or societies, both for people of all faiths as well as people with none.

As we discussed last month, people with a history of cancer who regularly attended a choir session showed evidence of improved immune function.